1. Technical Field
The present invention relates to an ink jet head.
2. Related Art
JP-A-2001-328281 discloses an ink jet head (hereinafter, simply called head) which has a black nozzle column discharging black ink and a color nozzle column discharging color ink and which performs color printing using black ink and color ink. The document further discloses a printer having the head.
The head disclosed in the document includes one black nozzle column discharging black ink and one color nozzle column discharging color ink. The color nozzle column includes a cyan nozzle block including a plurality of nozzles which discharges cyan ink, a magenta nozzle block including a plurality of nozzles which discharges magenta ink, and a yellow nozzle block including a plurality of nozzles which discharges yellow ink.
So-called bidirectional printing is effective for the case of forming dots spaced apart from each other at a pitch smaller than a nozzle pitch (a distance between neighboring nozzles) in a transportation direction of paper using a head having such a structure. This is because it is possible to print an image at high speed. The bidirectional printing means a printing method in which the head discharges ink while it travels in both the forward travel direction and the return travel direction.
However, the bidirectional printing has a problem in that positional misalignment between inks discharged from the head traveling in the forward travel direction and from the head traveling in the return travel direction is caused in the head traveling direction. That is, there is the probability that positions of formed dots are shifted in the head traveling direction. In this case, the positional misalignment of the dots significantly affects the quality of a picture according to kinds of images. Particularly, in the case of a text image and a line image printed in black, the positional misalignment of dots can lead to saccadic letters or lines. For such a reason, the misalignment of dots significantly affects the quality of a picture.